Photo-electric tube



A ril 5,1932. v p. J. JOHNSTON 1,852,808

PHOTO ELECTRIC TUBE Filed Feb. 1 1930 Inventor: Philip JIJohnstbn, 5 H1sAttorney.

Patented Apr. 5, 1932 I UNITED 1 STATES PATENT OFFICE PHILIP J.JOHNSTON, ,OFSCHENECTADY, NEW YORK, ASSIGrNOB, TO GENERAL ELEC- TRIOCOMPANY, A CORPORATION OF NEW YORK PHOTO-ELECTRIC TUBE I Applicationfiled February 1, 1930. Serial No. 425,324.

The present invention relates to apparatus sensitive. to light and moreparticularly to photo-electric tubes responsive to light of wave lengthsless than those of the v1s1ble spectrum, e. g., in the ultra violetreg1on,between 2000 and i000 angstroms. Rays of this sort are obtainedfrom specially construct'ed lamps of well known design and may beemployed for sterilizing and for promoting chemical and physical actionsin liquid and solid substances. In the employment of ultra violet light,it is often desirable to measure its intensity which necessitatesutilizing a device quantitatively responsive to the rays. It is knownthat certain of the alkali metals are affected by light, includingultra-violet, but when this material is incorporated in a bulb made ofglass as in the ordinary photo-- electric tube construction, the glassabsorbs the rays tosuch an extent as to preclude their transmission-inalarge degree toward the light sensitive material. Quartz is one of thefew substances highly transparent to ultra violet light but attempts tofabricate photo-electric tubes of this material have not heretofore beenentirely successful commercially due chiefly to the difliculty of makingin quantity electrical connection vwith the light sensitive layer.positioned within the tube. In order to make such connection, it isnecessary to fuse or otherwise secure the leading-in conductor to theinterior surface of the envelope. and in view of the exceedingly highmelting temperature of quartz (2200 C.) this has been found to beheretofore an impractical task.

An object of the present invention is to provide a photo-electric tubehaving a quartz envelope to the interior of which a rigid connection ismade in order to contact with the light sensitive material. A moregeneral object is to devise apparatus'which will efliciently translatelight energy of all wave lengths including the wave lengths which liebetween 2000 and 4000 angstroms into electrical energy suitable formeasurement purposes.

Theseobjects are attained in brief by providing a compression spring inthe leadingin conductor which contacts with the light sensitive layer soas to force the conductor continually against the surface of the quartz.

'It has been found that when the envelope is heated exteriorly ataposition corresponding to the place of contact between the conductor 0figure represents a viewj in elevation, partly broken away, of theimproved photo-electrio tube. I Referring to the drawing, numeral 1indicates an evacuated bulb of quartz or other material pervious toultra violet light and provided with a neck portion 2. A member 3,preferably of hard glass and suitable for forming a hermetic seal on thepump is attached to the bulb 1 by means of a graded seal 4 of well knownconstruction. The member 3 terminates in a reentrant stem 5 into whichare sealed conductors 6, 7 and 8. Between .the conductors 7 and 8 thereis a filament 9 constituted of silver or other suitable metal which isadapted to be evaporated when heated by current, the silver vaporspreading over and condensing on the interior surface of the bulb. Theconductor 7 carries a metal disc 9' which prevents de osition of thesilver on that portion of theulb in the rearof the disc, providing inthis manner a ing a hotflame, obtained for example from a quartz burnerso-called, on the exterior of the bulb directly below the point ofcontact. It is found that a portionvof the-platinum wire melts into aball 'or other shape of large surface and under the compressional forceexerted by the spring 11 adheres ten- .aciouslytothe interior of theenvelope making a rigid contact with the envelope. The combined effectof the heat and the force exermetal wire and a bod of quartz on accountof I the difiiculty of meltmg or fusing quartz and at the same timepositioning the leading-iii conductor rigidly in place within the bulb.While the exact nature of the joint obtained in this manner is notcompletely understood, I believe that it is due partly to anextraordinary high surface tension acquired during the localized heatingand perhaps a slight penetration of wire into the quartz. Whatever/bethe correct explanation, I have discovered that a contact made in thismanner is positively rigid and reproducible and is entirely practical inconstruction and operation.

After the silver or other metal has been deposited on the inner walls-ofthe bulb portion including the junction between the platinum wire andthe quartz, a highly reactive metal such as lithium or sodium may beintroduced into the tube. The reactive material is preferably providedin a metal tube 13 which may be attached to one of the conductors by apiece of stiff wire 14 and a support 15. The tube 13 is pinched at bothends and at the end to which the wire is secured is also welded. Beforethe tube 13 is closed, and prior to its insertion into the envelope,

the reactive material is introduced therein together with a binder suchas aluminum, magnesium or calcium. When the alkali-containing tube is inposition, high frequency currents may be induced therein from anexterbrly positioned coil (not shown) and the alkali vapor caused todistill through the end of the tube which is not welded, thereby tocondense. on the silver layer. In order to prevent current leakagebetween the leadingin conductors at the place where they emerge from thereentrant stem due to the condensation of alkali vapor at this place, aglass tube 16 maybe fitted about one of the conductors to increase theinsulation distance. If desired, an inert gas such as argon at a pres--sure o'f-about 75 microns of mercury may be admitted into the envelope.

In-operation, a voltage isapplied between the conductors 6 and 7 andwhen ultra violet or other'light having a wave length shorter than thatof the visible spectrum is allowed a to impinge on the alkali metallayer through the window 10, the impedance of the photoelectric tube islowered in-a degree corresponding to the intensity of the light. Whilethe utility of the quartz photo-electric tubehas been described inconnection with light having wave lengths below the visible spectrum, itwill be apparent'that the device may also be employed in the measurementof light of other frequencies.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is

1. A photo-electric tube comprising an envelope of quartz provided withan interior layer of a light-sensitive material, an electrodecooperating therewith and a leading-in conductor for said material, saidconductor being rigidly joined to the interior surface of the quartz egvelope.

2. A photo-electric tube comprising an envelope of quartz provided withan interior layer of light-sensitive material, an electrode cooperatingtherewith and a leading-in conductor for said material, said conductorbeing fused to the quartz.

3-. A photo-electric tube comprising an evacuated envelope of quartzcontaining a light-sensitive electrode and a cooperating electrode, apair of conductors passing through the envelope and connected with theelectrodes, and means for forcing the conductor connected with thelight-sensitive electrode against the inner surface of the envelopewhereby the conductor may be seured to the envelope at the place ofcontact.

4. A photo-electric tube comprising an evacuated envelope of quartzcontainin a light-sensitii 'e electrode and a cooperating electrode, apair of conductors passing through the envelope to furnish connectionwith the electrodes, and means for forcing the conductor connected withthe light-sensitive electrode against the interior surface of theenvelope whereby'the conductor may be secured to the envelope at theplace of contact, said means comprising a compressional springinterposed in the said conductor.

5. A photo-electric tube comprising an evacuated envelope of quartzcontaining a light-sensitive electrode and a cooperating electrode, apair of conductors passing through the envelope and connected with theelectrodes, spring means for forcing the conductor connected with. thelight-sensitive electrode against the interior surface of the envelope,and means for rigidly joining the conductor with the quartz at the placeof contact.

6. The method of securing a metallic wire

